Generic-ballot polling update on US Congress

Charles, at Political Arithmetik, has two new reviews of the generic party polling in advance of the congressional elections. At least two striking findings for me are: (1) the range of variation in these polls is substantial, and (2) so far, at least, the recent increase in presidential approval is having little or not effect on poll-respondents’ congressional partisan preference.

With caveats about the variability, Democrats still enjoy more than a ten-point advantage.


Click on “US vote ’06” above to see the previous discussion of these polls and the difficulty of translating them into actual votes for actual candidates, and into an ultimate seat distribution.

Generic US House polling: What does it tell us?

Charles, at Political Arithmetik, has one of his many must-read, must-view posts–this time, about trends in 2006 and past cycles in polling for US House.

As Charles notes, Democrats tend to perform much better in this polling than in the actual voting, where real candidates–including known incumbents–are running, rather than just the “vote for party” option that the polling simulates. Even so:

In no cycle since 1994 has the Democratic lead approached 10%, let alone exceeded it. So by the standard of “relative lead” in the generic ballot, 2006 reflects extremely strong pro-Democratic forces.

The current trend of several poll shows an average lead for the Democrats of almost fifteen percentage points! And it has been trending mostly upward for some time.

Of course, as Charles also notes, it is not only fraught with peril to go from generic polling to estimating the actual aggregate congressional votes, but even more peril lies in estimating seat swings based on (expected or even real) aggregate votes. But such peril never stops F&V!

I posted some graphs of votes and seats trends over time here three months ago.* If Democrats really had a 15-point lead in national votes, that would mean around 54% of the vote (allowing for the recently typical 5% or so for third parties). Extrapolating from the graph (see link below), that would put the Democrats anywhere from about 240 seats (at the lower responsiveness of recent elections) to about 265 (using the trend over the entire post-1945 period. which is probably less likely to be relevant). (Those are ‘eyeballed’ point estimates off the graph; I think it is pointless to talk about margins of error, as long as we all understand that these are just rough estimates of what would happen if the votes translated into seats in 2006 more or less as they have in the past–whether the very recent past, or the past six decades.)

Of course, we should not assume the polling will accurately translate into votes. As Charles shows, it does not, or else Democrats would have won each of the last six House elections. (Even 1994, Charles shows, the Democratic party had recovered from its earlier generic-polling deficit by election day!). (They did win 1996, in votes, though not in seats.)

The following list shows, for each year since 1994, the final polling difference (always D-R), the actual difference in percentages of the total vote, and the actual difference in the two-party vote. Data on the polling are from Political Arithmetik. Actual votes data are from my files (based on Clerk of the House reports).

The last number, in parentheses, is simply the difference between the final two-party vote and the final generic polling result. (I much prefer to use the shares of the total vote, but pollsters, in their infinite wisdom–and for that matter, most of the country-specialist political scientists–ply their craft as though there were literally only two parties.)

    1994, +3.35, -6.79, -7.05 (+10.4)
    1996, +5.45, +0.30, +0.32 (+5.13)
    1998, +8.03, -0.89, -0.93 (+8.96)
    2000, +5.26, -0.34, -0.36 (+5.62)
    2002, +1.49, -4.62, -4.88 (+6.37)
    2004, -1.07, -2.76, -2.88 (+1.81)

So, on average, the final poll has overstated the Democratic party vote advantage by 6.38 percentage points! (Note that the one year when the polls showed Republicans ahead was also the year with the smallest error of estimate, while the year the Republicans took control of the House from the Democrats was the year with, by far, the greatest error from poll to actual votes.)

If we take Charles’s current average of generic polls (+14.65 Dem) and subtract the average difference between final polling and actual votes (6.38), we would have an estimated Democratic advantage of “only” +8.27. That would be roughly 51.6% votes for the Democrat (again allowing around 5% “other”). Now, doing our perilous extrapolations, we get a range of anything from around 225 seats (a bare majority, assuming the votes-to-seats conversion will be as nonresponsive as it has been in the last decade) to around 245.

Of course, if the generic trend continues upward for Democrats, it would become quite unlikely that they would not be the majority party in the next House. On the other hand, the relative nonresponsiveness of the current House electoral system to votes swings would suggest that even a small recovery for the Republicans in the generic polling by early November could keep the current majority intact.

No, we can’t make any predictions, unfortunately. It looks bad for the Republicans. You already knew that. But Democrats could fail to capitalize on their current good polling. You probably aleady knew that, too. What I hope this discussion shows is that a failure to “capitalize” would not necessarily be from bad tactics (as the media will tell us), but from underlying structural features of the US House electoral system. To review, those are (not necessarily in order of importance):

    1. Voters vote for candidates, not parties.
    2. The party polling tends to overstate voter preferences for living, breathing Democrats, and has done so for many years (even in 1994).
    3. The process of allocating House seats is not as responsive to vote shifts as it once was.


* “Votes and seats in the US House,” and

“Presidential approval and midterm vote and seat loss.”

Lieberman is toast

… well, at least as a Democrat.

[Note: Revised and exended below]

Political Arithmetik has the details, which surprisingly include a collapse for the Senator among moderate and conservative likely Democratic primary voters.

Leaverman” will run as an independent if he loses Tuesday’s primary, given that Connecticut lacks a “sore loser” law.

If he then wins in November–as is likely–maybe he will hold the balance of power in the Senate, giving a whole new meaning to “Joementum.”


UPDATE, 4 August: A poll by Quinnipac released yesterday has Lamont 54%, Lieberman 41% in the primary. The linked story also says:

Lamont supporters are touting the notion that with a big enough Lieberman loss on Tuesday — if Lamont gets 60 percent of the vote, for instance — the senator will be forced to yield to pressure from party leaders and drop his independent bid.

That sounds like wishful thinking to me. However, if the interest groups that currently support Lieberman were to defect upon a convincing primary win by Lamont, then Liberman could find himself without the support needed to carry on his sore-loser independent campaign. Still, with a very weak Republican candidate, there would be little risk from a continued Lieberman campaign; that is, little risk that his independent bid would tip the seat to the Republicans. Consider what the same poll shows if a three-way general election were held today:

if Lieberman were to run as an independent, he would get 51% of the vote to Lamont’s 27%. The Republican challenger, Alan Schlesinger, registered 9% in that poll.

The party registration numbers make a race between the two Democrats in the general election viable: 50% nonpartisan, 30%D, 20%R. (That sums to 100%; does Connecticut law protect the associational rights of only two state-sponsored parties?)

How many Senators won less than 59% last time?

In the previous post, I noted that there were thirty-nine Republican House members who won by margins of less than the 9-point swing against the party that we saw this week in the special House election in San Diego County.

How many Republican Senators whose seats are contested this fall won with less than 59%? Five. (Not enough to swing that chamber given that a Republican holds the Vice Presidency and this the tiebreaking vote.) Continue reading

What if the Bilbray-Busby race were to be typical this November?

The Republican party won the 50th House race in California in this week’s special election. However, it suffered an approximately 9-percentage-point negative swing, compared to November, 2004.

How many current Republican House members would lose their seats if they suffered a 9-point swing this November?

    Thirty-nine.

Their current majority?

    Fifteen.

(By the way, 39 might not be as ridiculous as it seems. A late-May Cook Report said 36 GOP seats were now in play, and another 11 were toss-ups.)

If there were an actual 9-point national swing in votes away from the party, they would lose a lot more than 39 seats. While swings are never uniform across all districts in plurality systems–even less so in the USA–and thus some of Republicans within the 9-point margin last time would survive and a Democrat or two would lose, such a national swing would also take down many Republicans whose margins last time were much greater than 9%. Why? Because the swing would be concentrated in the seats that the GOP won with less than 15-20 points and would hardly affect seats won by larger margins,* due to the endogeneity of party effort and voter interest this time to margin last time.

My previous analysis would put the GOP’s seats from 40% of the vote (which is where it would be after a 9-point swing) at somewhere between 130 (using the whole 1946–2004 period votes-seats relationship) and 175 (extrapolating from the much less responsive electoral system of the last decade).

In other words, if this formerly safe Republican district in San Diego County were to be a bellwether, not only the majority, but the two-thirds majority of the House would be in play.

Thus Republicans can’t be too gleeful about the outcome of the special election. They won the seat, but this could give a whole new meaning to that Rumsfeldian concept of catastrophic success.

* Almost 80% of House seats in 2004 were won with margins greater than 20%, including (by my count) 185 of the 232 seats currently held by the GOP. One of the lessons of 1994 is that even a handful of these could swing if there is a strong national tide against the incumbent party.

Republicans hold Calif-50 House seat

[UPDATED (13 June) as final results continue to trickle in.]

With 100% of precincts accounted for, preliminary results show the 50th House district in California held by the Republican party in the 6 June special election.

    Brian Bilbray (R), 49.66%
    Francine Busby (D), 44.96%
    Bill Griffith (ind), 3.79%
    Pail King (Libtn.), 1.60%

Bilbray’s margin was just over 4400 votes.

Busby won just over 68,000 votes, or roughly 8,000 more than in the first round in April, when turnout was slightly lower. Turnout in the district’s runoff was reported to be around 42% (a few percentage points higher than in the rest of the County, as well as a few percentage points higher than in April).

Bilbray’s 49.7% is almost four percentage points worse than the whole field of 18 Republican hopefuls got in April, but it was enough.

Former Congressman and now Convict Duke Cunningham beat Busby, 58–36, in November, 2004.

In the second division of the special election, the Libertarian more than doubled his votes from round one to the runoff and Minutemen-endorsee Griffiths more than quadrupled his votes.

After the first round, when Busby won 43.8%, I said:

Nearly 44% of the vote for a Democrat in this district is impressive. But that moral victory still looks to me like the only kind she will get.

While my post on election day gave some scenarios in which she might win, she and the party indeed will have to settle for the moral victory–at least for now. She gets another crack at Bilbray (who won 54% in the concurrent closed Republican primary) in November.

The ingredients of a Democratic takeover of Congress

A pretty good AP story on this theme just came off the wire, although I would say the things they list as a sequence of three (implicitly saying all are necessary) really look to me as “or” in that any one of them should suffice:

First step: Voters must focus on the national landscape on Nov. 7 rather than local issues and personalities that usually dominate midterm elections…

Second step: Voters must be so angry at Washington and politics in general that an anti-incumbent, throw-the-bums-out mentality sweeps the nation…

Third step: Americans must view the elections as a referendum on President Bush and the GOP-led Congress…

In the current context, any one of these should be enough; in fact, any one of them ought to indicate the presence of the other, meaning they are not “steps.” How could you have a national election that was not a referendum on the ruling party, and how could that not be anti-incumbent when that ruling party is as discredited as it is right now?

As for the likelihood of such a nationalized swing, I reviewed that with some graphs a little while ago.

Votes and seats in the US House

In the previous planting on presidential approval and impact on House votes and seats for the president’s party, I noted there was no evidence that the translation of votes to seats had become less responsive to changes in votes totals (as might be expected from gerrymandering or other trends making House districts more homogeneous).

However, when we look at the scatterplots of each election since 1946, we might draw a different conclusion. This first graph shows Republican votes percentages and seats won in the House.

Rep_votes-seats.jpg

(click on the image for a larger version in a new window)

The horizontal line shows 218 seats, a majority. The diagonal is a best fit. There is not a lot of scatter around the best fit–consistent with my statement in the earlier post that the relationship between the popular votes and House seats is more predictable than I might have imagined.

Now, for the sake of comparison, here is the same graph for the Democratic party.

Dem votes-seats.jpg

Less here stands out as anomalous, at least to me. Not even the recent elections. (The one outlier at 260+ seats on 48% of the vote, which I forgot to label, is 1948.) However, the best-fit line is a bit less steep: Democrats, over time, have gotten a bit less payoff (or decline) in seats from any given gain (or loss) in votes. (Partly this may be a diminishing returns phenomenon, given how dominant the party’s votes majorities were for many years.)

Now, let us return to the Republican graph. Despite an overall tendency for seats to follow from votes in a fairly predictable way, it is clear that recent elections are deviating from the pattern. Every election since 1996 is above the trend. More to the point, in each House election since 1996, the Republican party has won a majority of seats on less than 50% of the vote. The only time that had happened before was in 1952. In 1996, as well as 1952, the Republican party did not even win a plurality of the House vote.*

With all due caveats about the small number of data points (5), if we eyeball a best fit to the 1996-2004 data, the line is clearly much less steep than the overall trend, suggesting that today’s Republican party can afford to lose vote share and yet retain the House majority. It could fall to 47% (in 2004 it was 49.3%) and possibly still have at least 218 seats. Nonetheless, such an outcome is not very likely. Part of what allows the Republicans to retain a majority on less than 50% of the vote is the growth in recent elections in third-party voting. If 2006 is going to be a change year, and if the Republican vote falls to 47% (or lower), it is highly unlikely that the third-party vote will rise (it was 4.2% in 2004) enough to keep the Democratic party from enjoying a plurality of a few percentage points. (Compare 1994, when the third-party vote share was 3.7% after having been 5.3% in 1992.) Is the House so gerrymandered or would the regional vote swings be so skewed as to allow a Republican majority if the votes were something like 50-47 in favor of the Democrats? I don’t think so, though it is certainly possible.

* In 1952, Democrats actually had a majority of the vote, yet Republicans won a majority of seats.

UPDATE: Readers interested in these themes will find Jack’s post at the Fair Vote Blog, linked in the comments below, to be of interest. I think the hypotheses that Jack is referring to can be tested only at the district level and over time. I hope to look into this, although the district-level data I have contains no third-party votes, and as I allude to above, it is clear that growing third-party voting is at least part of the picture of “skew” in the sense of regional and partisan biases. It would be quite an effort to assemble district-by-district data on all candidates and not just those with R or D by their names. The country specialists who study the US House simply throw out anything that is not D or R. We comparative electoral systems specialists know that doing so is likely to miss something important–or at least prevent the opportunity to find out if other party voters are making a difference.

If anyone knows of machine-readable data that includes all candidates, please tell!

Presidential approval and midterm vote and seat loss

What is the relationship between a president’s approval in the spring and his party’s House seat loss/gain in the upcoming midterm election? Charles Franklin discusses this question at Political Arithmetik. Approval in late April of around 36.5% (approximately where Bush was then) translates into a point prediction of around 45 seats lost. However, as Charles notes, and as one can learn through the application of interocular tools to his accompanying graph, the error on this estimate is quite large.

It is worth noting that 1994 is one of the biggest outliers, in that the Democratic party lost “too many” seats for the level of approval the public registered that spring for President Clinton. Of course, in 2006, with a swing of only 15 seats required to change control of the House, the Democrats do not need to over-shoot the estimate; they just need to avoid under-shooting it too much.

Quite apart from other factors that might lead to an over- or under-shooting of the estimated seat loss for a given approval level, there is no direct causal mechanism that links these two variables. The more proximate link is between approval and the president’s party’s vote share in the midterm election. Then a second stage translates any change in House votes into some level of change in House seats. One of our specialties here at F&V is votes-to-seats translation, and Charles was kind enough to share his data. So, let’s combined the approval and seat loss data with the national votes data and see what we get.

The first graph shows approval in late April/early May and change in House votes for the president’s party.

pres-approv_vote-chg.jpg

(Click the image to open a larger version in a new window.)

The 1950 election stands out as an outlier, but otherwise, there is clearly a trend in the expected direction: lower approval, more vote loss. Still, the scatter is hardly trivial. The 1950 election is an odd one. President Truman’s Democratic party lost seats (-29), even though it gained votes (+1.6). Truman’s approval was 41% at the beginning of May. Part of the reason for the Democrats’ vote gains was the high “other” votes total for the House in 1948, a year in which Strom Thurmond and Henry Wallace ran third-party campaigns for president. (Most analysts of US elections use the two-party vote, but I hate to throw data out; third parties are part of the picture in some elections. As a share of the two-party vote, Democrats indeed lost votes–very slightly.)

A statistical regression on these 14 data points shows–nothing. However, if 1950 is excluded, we do get a significant result. I will leave it to readers to decide if it is valid to exclude 1950. It is clearly is an outlier in a way that no other midterm election is, and it has the biggest movement in the past quarter century from one election to another in the the third-party vote. I think both of these factors make it valid to remove.

Simulating from the regression (without 1950), approval in April/May of 36.5% (Charles’s estimate for late April) predicts a vote change of -7.2, and a 95% confidence interval of -10.3 to -4.0. That is a rather big confidence interval, but the data are what the data are. Approval of 40% predicts vote change of -6.4 (-9 to -3.8); 50% predicts -4.3 (-5.7 to -2.8). The midterm loss phenomenon is a striking consistency in US politics (and, as my research has shown, that of other presidential systems, too): only with approval of 65% does the outer limit of the 95% confidence interval turn positive on the party’s vote change.

But control of the House depends only indirectly on the national vote share. Is there a systematic relationship between vote change and seat change in US House elections? I was prepared to find the answer to be not much, but actually there is. The graph below shows the relationship.

US House votes-seats.jpg

Again, 1950 looks a bit odd. So does 2002, one of only two US midterm elections since the Depression in which the president’s party gained seats. (The other was 1998, which looks fairly “normal” here, given that the Democrats in that year gained votes). In fact, it is worth noting that the way in which 2002 is “odd” is that the Republican party should have gained more seats. The party gained 3.3 percentage points over its 2000 House vote, yet gained only 8 seats. A regression on these data (again minus 1950) suggests the Republican party “should have” picked up around 20 seats in 2002, though the confidence interval is again large (4 to 36), and the 8 that they picked up is well within the 95% interval.*

So, if the Republican party loses 7.2 percentage points off its 2004 House vote share (the point prediction from 36.5% approval), it would be predicted to lose 49 seats (with a 95% confidence interval of -60 to -37). Even 37 is probably well beyond the worst fears of Republicans (though Rep. John Murtha (D-Penn.) predicted yesterday that his party would gain 40 to 50). The low-end estimate of the impact of 36.5% approval on the vote share (-4%) predicts a loss of 27 seats; even the most GOP-favorable end of the 95% confidence interval is 20 seats, which would be enough to shift control of the House.

In fact, any vote loss for Republicans of around 3.5% or more results in an estimate, even at the most GOP-favorable end of the confidence interval, of enough seats to shift control of the House. I am not in the prediction business, such a swing in votes strikes me as quite minimal: a 3.5% vote loss would be well within the margin of error of estimate even for a president with 50% approval.

There is one final analysis to make on these data. It is widely believed that House elections are less sensitive to national trends nowadays than they were decades ago. So we should consider whether there is a time factor to these estimates–both for the relationship between approval and votes change and for that between votes change and seats.

The short answer is that there is a substantial time effect on the first link, but none at all that is discernible on the second. In other words, the president’s party in the House is indeed more sheltered from assessments of the president than was once the case, as would be expected from the “personal vote” perspective or the incumbency advantage, or any models of voter choice that say that, for whatever reason, people tend to want different things from their president and their member of the congress nowadays, and more so than in the past. However, the absence of any time effect on the votes-seats relationship offers no support to claims that greater district homogeneity (from gerrymandering or any other factor) has made individual members more sheltered today than in the past. (And, yes, I am aware that this goes against much of the literature in my profession; I am just reporting what these data show, with due caveat for the substantial error of these regression estimates, as I have been noting throughout.)

To put this time analysis in real numbers (OK, estimates), in 1960 the party of a president with 50% approval in early May would expect a votes change of -5.65 (-7 to -3.9), while in 2004 such a party would have expected a vote change of only -2.1 (-4.3 to +0.2).

A president in 2004 with early May approval of 36.5% (such as the 2006 incumbent) could expect his party’s votes change to be -4.9 (-8.2 to -1.4). If the GOP can keep its vote losses to the more favorable end of that confidence range, it may be able to hang on to control of the House.

None of these statistical techniques allow us to predict what is going to happen in 2006, but they do tell us that the Republican party, if it can’t enjoy a substantial approval rally for its president, needs an unusually low linkage between that approval and its party vote share and/or an unusually low impact of the votes on the seats, in order to hang on. It’s a tall order.


*At zero change in votes, the estimate of seat change is indeed zero (actually -0.199), as it should be, and the 95% confidence interval is ±10.

US House CA-50 update: Bilbray and Busby tied, Roach sort of running, sort of not running

In the special election for California’s 50th US House district seat, a poll has Republican Brian Bilbray and Democrat Francine Busby in a dead heat. Meanwhile, Eric Roach, who narrowly lost the Republican nomination to Bilbray on 11 April, is not “aggressively” seeking to defeat Bilbray for the nomination for the regular general election contest in November.

An automated telephone poll by Survey USA, puts Bilbray and Busby each at 45% among “likely voters,” with 9% saying “other”1 and 1% undecided. The sample was 442 voters, and the margin of error was 4.8 points.

Roach will be on the ballot for the Republican primary, the same day as the runoff between Bilbray and Busby (and a few minor candidates). The runoff will fill the seat through next January, while the primary will decide the candidates for November’s election for the full-term seat. With much pressure from national Republican leaders, Roach says:

I do not believe it would serve the interests of the conservative majority to campaign aggressively against the Republican special nominee.

Apparently, Democrats were hoping Roach would be “aggressive,” and Republicans feared disunity would help Busby.2 However, I wonder if Republicans’ chances of holding the seat in June would not be better if Roach stayed in, and better still in November if Roach were the nominee against Busby.

I think there is little doubt that in a closed primary, Roach would have defeated Bilbray, who does little to excite the base and even holds some moderate/liberal views on some key issues for the right, as well as holding the baggage of a former congressman (from an only partly overlapping redistricted seat) who became a lobbyist. The race for the Republican nomination in April was very close and featued multiple contenders, and any voter could vote for any candidate, regardless of party affiliation. In June, only registered Republicans or voters registered “delcine to state” who specifically request a Republican ballot may vote for the party’s November nominee.

And then there is the always-important factor of turnout. If Republican turnout is depressed in June (and November) and Democratic turnout is energized–as now seems likely–a campaign by Roach could bring more “base” Republicans out to vote.

The Survey USA poll contains some evidence for this, claiming that among voters it defines as “likely” who did not vote in April, Bilbray leads Busby by 19 points. That lead looks fishy to me, but it suggests there is a pool of Republican voters who skipped the primary; if they skip the next two elections as well, Republicans might very well lose the seat–a previously “safe” seat.

The inactive campaign by Roach is probably good news for Busby.

I do not watch a lot of local television, but one does no thave to watch much to see that both national parties are aggressively attacking the other’s candidate. Obviously, Republicans are scared and Democrats smell blood.


1. The actual “other” candidates in the runoff are far too insignificant to have real support of 9%. I wonder how many of these are Roach supporters who do not understand the confusing ballot, with a general (in which Roach is not running) and primary (in which he is) side-by-side.

2. The third-pace finisher in the race, former state assembly member Howard Kaloogian, said he would endorse Roach if he continued the challenge

CA-50: Bilbray may face nomination challenge in June

Republican Brian Bilbray, who will face off against Democrat Francine Busby (and two minor candidates) in June to fill the remainder of Duke Cunningham’s 50th US House term, may not have a clear path to his party’s nomination for the full term to be decided in November. On the same day as the special-election runoff, there will be a primary for November. Eric Roach, narrowly defeated by Bilbray for the Republican runoff slot, may enter the June primary, and Howard Kaloogian–who came in third among Republicans–may endorse Roach.

Given that Bilbray could be seen as a weak candidate,* and given that he won only 28.5% of the total number of votes received by Republicans in the first round, it would be surprising if no one were tempted to challenge him for the nomination. In June, unlike in the April vote, only registered Republicans and independents who specifically request a Republican ballot, and not Democrats, will be able to participate in any contest among Republicans for the right to bear the label in November.

*Former and not very distinguished congressman from a (mostly) different district, with a moderate voting record on many key Republican issues, and now a lobbyist.

Click here for the full set of posts on the 50th race and other aspects of the 2006 congressional elections.

Regional patterns and turnout in the 50th district

From the past week or so, a couple of reports from the North [San Diego] County Times have looked at the turnout and regional patterns within the CA-50 House district special election.

The final tally shows the turnout was 39% of registered voters. That may not sound like much, but it is actually quite high for a special House election. Turnout apparently was higher in the coastal communinities, which are precisely the areas in which Democratic candidate Francine Busby was strongest.

In many midterm elections, when the party in control of the House changes (as in 1994), or when it defies the usual midterm-loss phenomenon and picks up seats (as in 1998 and 2002), turnout is typically one of the decisive factors. Is the 50th district turnout pattern significant? Does it show an energized Democratic party and unenthusiastic Republicans? Or will it be an aberation? The answer to these questions will go a long way towards determining which party is in control of the US House as of next January.

A second report shows a map of the top three candidates’ support in various communities.* It shows that Busby won majorities in the coastal communities of Encinitas (a small subset of which is Cardiff, where she is an elected school board member) and Del Mar, as well as in the slightly inland sprawl-town of Del Mar Heights. The three top candidates ran almost even in the wealthy enclave of Rancho Santa Fe, where 24% of the vote was far below Busby’s overall district share (44%). In the inland communities Busby ran slightly below (or, in the case of Escondido, well behind, at 35%) of her district overall share.

*I was going to post it, but it is rather small and blurry. It was a lot easier to read in the print version than on-line.

US House marginal seats and Democrats’ prospects in 2006

This graph (click image for a larger version) shows, with the dark line, the number of US House seats that were won “marginally” in any given election from 1946 through 2004.

US House marginal graph.jpg

This takes a rather generous definition of what is “marginal”: Any seat that the party holding it won with no more than 60% of the two-party vote. The grey line is the number of seats the “out” party would have to win in the next election for control of the House to shift.

The trend shows clearly the decline in the number of relatively close seats in recent years, although it also shows that the current low number of marginal seats is not exactly unprecedented. There were 75 seats won with 60% or less in 2004, but there were 66 such seats in 1988. Following the 1988 election, there was a sharp uptick in the number of marginal seats, and when Republicans finally took the House in 1994, there were 162 seats that had been won at the previous election with less than 60%. The number of marginal seats has declined steadily since the Republicans took control.

While the low number of marginal seats in the current House is bad news for Democrats’ hopes of retaking the chamber, the good news for them is that the majority they are fighting against is much narrower than that which the Republicans faced heading into the 1994 election. In 1992, Democrats had won 258 seats and Republicans 176, meaning the out party needed to win of at least forty-two new seats. They got fifty four. (Actually, they took 58 seats from Democrats, but 4 other seats swung in the reverse direction.)

In 2006, Democrats need a net swing of only fifteen to retake the House (counting Bernie Sanders’ seat in their column, and assuming they hold it as he vacates it for his Senate bid).

If we break the marginal seats down into those held by the current majority versus those held by the “out” party, we see that the Democrats’ order is a bit taller than was the Republicans’ was in 1994, though this “tall order” is somewhat compensated for by the narrowness of the current Republican majority (noted above).

Despite the “sweep” pulled off by the out party in 1994, the Republicans actually won less than half the “marginal” seats. There were 90 seats that Democrats had won with 60% or less of the two-party vote in 1992, and Republicans won 40 of these. (They also won 18 seats that the Democrats had won with more than 60%.)

The national two-party vote swing from 1992 to 1994 was just over six percentage points. If swings were relatively uniform, we would expect nearly all the seats that Democrats held with less than 55% of the two-party vote to have swung. But even these more-marginal seats–46 in all–swung at a less than 50% rate: Republicans won 22 of them. This underscores the extent to which House elections in the USA are fundamentally not national partisan contests to the degree they tend to be in parliamentary systems: Even in a year branded by pundits as a “revolution,” the erstwhile “in” party kept a majority of its marginal seats. (I hope to post some parliamentary-election swings for comparison at some point.)

As for 2006, of the 75 seats won with less than 60% of the two-party vote in 2004, forty-seven of them are held by the “in” party (Republican) and 28 by the “outs.” When we look at the seats won last time with 55% or less, the two parties are defending an equal number of such close seats: ten each.

If the Democrats in 2006 were to win just over a third of the seats that the Republicans won in 2004 with 60% or less, they would retake control, provided they did not lose any seats of their own.

With Democrats running about 8-10 points ahead in most recent generic partisan polls and with the Democratic candidate having gained eight points in a (previously) very safe Republican district in the recent special election in California, an alternation in the majority party is feasible. But, given the low number of marginal seats being defended by the majority, the Democrats can’t be any less successful than the Republicans were in 1994 at nationalizing the election. And these data show Republicans were less successful at that task than the conventional wisdom might lead one to believe. Nationalizing congressional elections in the USA is just very hard to do.